Fluid driven tank cleaning apparatus are well known. For example, U.S. Pat. Nos. 5,172,710; 5,169,069; 5,092,523; and 5,012,976 all relate to a line of fluid driven tank cleaning machines sold under the name GamaJet.RTM..
It is known in the prior art to provide gear trains that convert the flow of pressurized fluid into motive power for rotating tank cleaning machines. These gear trains are typically spur gears or pinion and ring gear trains. An epicyclic nozzle drive is disclosed in U.S. Pat. No. 4,244,524--Wellings. The gear train is in the path of the input fluid stream and this fluid is used to lubricate the drive and dissipate heat. The reduction achieved by the epicyclic gear train is 156.8:1, and the disclosed device operates at pressures of about 300 psi. The Wellings patent admits that the device is simply an existing prior art nozzle (Sellers "Jumbo" Model 215 S), with the prior art harmonic drive replaced by the epicyclic gear train.
U.S. Pat. No. 3,275,241--Saad discloses a tank cleaning apparatus where the input stream rotates an impeller and then exits into the nozzle. A shaft extending from the impeller transfers its rotation into a gear box using a worm gear, and the gear box provides two axes of rotation. The gear box is sealed from the cleaning fluid flow.
Currently available apparatus, however, require a relatively large size opening for insertion into a vessel. U.S. Pat. No. 3,637,138--Rucker recognizes that the problem of providing a reduced diameter cleaning apparatus is difficult to achieve by merely reducing the size of existing components, and suggests that using planetary gear drives, such as those shown in U.S. Pat. No. 3,464,632 (Bristow) results in a device that is not reliable. Rucker also refers to U.S. Pat. No. 3,326,468, also by Bristow, which does not use a true planetary gear train, but simply uses a small pinion gear (FIG. 3, 102) to turn a ring gear (104).
U.S. Pat. No. 4,351,478--Looper recognizes that prior art cleaning devices do not fit into the relatively smaller openings of multiple compartment tank cars, and proposes as a solution a device that uses a separate air motor to turn the device. The air motor and associated equipment remain outside the vessel during cleaning, thereby permitting a reduction in the size of the cleaning head. Similarly, U.S. Pat. No. 4,214,705--Watts et al. recognizes that size reduction is desirable, and discloses a device having a separate air motor to drive part of the cleaning head. Another cleaning device uses a separate pneumatic, electric or hydraulic drive motor to rotate the cleaning head is disclosed in U.S. Pat. No. 3,834,625--Barthod-Malat. The design is said to avoid the problems caused by using high pressure fluid to drive the mechanism, i.e., the high pressure fluid causes the mechanism to rotate too quickly. A planetary gear train is used for one axis and a worn gear for the other.
On the other hand, U.S. Pat. No. 3,874,594--Hatley suggests using a single driving means, such as a turbine, powered by the washing fluid to rotate a cleaning machine about two axes. The disclosed device fits into smaller ports by connecting the nozzle and its worm drive at the end of a long shaft that is in turn connected to gearing that drives the shaft about its axis. This reference also teaches that the ratio of the rotational speeds between the axis is constant, but can be varied by a "program" determined by the profile of a cam. An alternate embodiment disclosed by the Hatley patent uses a drive mechanism for the entire cleaning head that is moved to the vicinity of the nozzle, i.e., inside the tank. The required gear reduction is achieved through a train of bevel gears, and a planetary spur gear 53 transfers the impeller rotation to a worm gear that drives one of the axes of rotation.
Finally, U.S. Pat. No. 3,88,740--Sugino et al. recognizes the need for washing apparatus of reduced size that fits through smaller access opening and the problems that arise when such mechanisms spin a too high a rate. The disclosed device, however, uses the reaction forces of the cleaning fluid exiting the nozzles to rotate the nozzle head, which in turn rotates a trochoid pump to provide a gear reduction to rotate the body of the device. Thus, in contradistinction to many other prior art devices, the cleaning fluid does not drive an impeller.
From the foregoing, it is clear that there is a long-felt need for reliable mechanisms that can provide sufficient gear reduction in rotary spray cleaning heads. Certain prior art references disclose limited uses of planetary gears, and the Bristow patent teaches that such gear trains are unreliable. The Sellers reference discloses a planetary gear drive, but teaches that it is important to flow the cleaning fluid around the components in order to provide lubrication and heat dissipation. For this reason, the planetary gear drive disclosed in Sellers is disposed between the impeller and the outlet to the nozzles.
Additionally, the prior art recognizes and offers various solutions for the problem of providing a spray cleaning head that can fit into openings of reduced size. Many of the references suggest using remote drives or separate motors that are not located in the vicinity of, or part of, the cleaning head, or that do not use the cleaning fluid as a source of motive power. The prior art further recognizes that this problem is difficult to solve, since existing devices cannot simply be scaled down to size.